Level vials of various types are used in a wide variety of control systems in which the orientation of a machine element is measured and controlled. Typically, the vial is secured to the machine element. The vial moves with the element and provides an electrical output or outputs that indicate the orientation of the level vial and the machine element with respect to at least one axis. Such level vials may, for example, form a part of a system that controls the orientation of a laser beam transmitter and the orientation of the beam produced by the transmitter. Preferably two level vials are included in a transmitter of this type, with each vial providing an indication of orientation of the transmitter with respect to one of a pair of substantially orthogonal axes.
Typically a level vial includes a glass or plastic vial casing that defines an elongated fluid chamber. The chamber has a curved upper surface which slopes downward, away from the center of the vial. The chamber is partially filled with fluid so that an air bubble is trapped in the chamber with the fluid. As the level vial is tilted about a generally horizontal axis, normal to the direction of elongation of the chamber, the bubble in the vial moves across the curved surface of the chamber toward the more elevated of the two ends. The degree of movement of the bubble is an indication of the orientation of the vial with respect to the horizontal. Various arrangements have been used to detect the position of the bubble and to produce an electrical signal that is dependent upon the orientation of the level vial and therefore indicates the orientation of the machine element.
One type of level vial comprises an electrically nonconductive vial casing, usually made of glass, that defines an elongated, arcuate chamber which curves generally downward toward its opposite ends. A quantity of electrically conductive fluid is provided in the chamber. Such a fluid may, for example, have a ketone component. A pair of end electrodes electrically communicate with the upper portions of the chamber adjacent its opposite ends and extend toward the central portion of said chamber.
A common electrode extends substantially the entire length of the chamber along its lower surface. The air bubble in the chamber rises to whatever portion of the chamber is uppermost. It will be appreciated that, as the vial is tilted in one direction, the electrical impedance of a path from one end electrode through the electrically conductive fluid to the common electrode will increase, while the electrical impedance of a path from the other end electrode to the common electrode will decrease. When the vial is tilted in the opposite direction, the end-electrode-to-common-electrode impedances change in the opposite fashion. While this level vial arrangement functions well, it requires that lead connections be provided both above and below the level vial. This, in turn, means that all associated components cannot be mounted on a single circuit board. Additionally, two such level vials are required to assess the orientation of a machine element about two horizontal axes.
Other level vials use a photo-optical arrangement for detecting the position of the bubble in the fluid chamber. In one such arrangement, a light source emits a beam of light which passes through the chamber and is detected by a pair of photodetectors adjacent opposite ends of the vial. As the bubble moves toward one of the ends of the vial, the amount of light reaching the photodetectors is changed, and the relative electrical output signals from the photodetectors provide an indication of the degree of tilt of the vial. This level vial arrangement has the disadvantage of requiring components above and below the vial in order to determine the position of the beam. The disadvantage of this arrangement is that it requires that a light source and photo-detectors, and their associated electrical connections, be provided both above and below the level vial. As with the other type of level vial discussed above, this means that all associated components cannot be mounted on a single circuit board. Additionally, two such level vials are required to assess the orientation of a machine element about two horizontal axes.
It is seen that there is a need, therefore, for a level vial construction in which all of the electrical components can be mounted on a single circuit board, and for such a level vial construction in which inclination with respect to two substantially orthogonal axes may be measured with a single level vial.